not sure what the laws are like where you live, but here in SoCal there is only one form of the PPG primer available. its still the DP series of epoxy primers, but they have the LF Suffix on them. DP90LF and whatnot. ( they also have DP40LF and umm... DP50LF i think, the only difference is color. ) The DP90LF is a black epoxy primer and will work well to seal out the moisture and will bond to the metal without the use of an etching primer. the corrosion resistance will come in handy if you will not be completing the car in a short amount of time as well. dont count on it too much as a great surfacer, but you can pile something else on top of it if you need to. its really nice stuff.
The LF stands for Lead Free. if you can get the original stuff, hey, go for it. im all for VOCs and Chromates ha ha. its just not legal here in SoCal. but hey, i painted one of my cars with a 4.2 VOC clearcoat that i still can get any time i want.
oh yeah, i work at a paint shop and sell primers, paint and other crap all day long.